In the field of radio communications, transceiver products are available which package a radio antenna along with the electronics necessary for its operation to provide convenient wireless, radio transceiver capabilities. For several reasons, such products are often subject to conflicting size requirements. For example, it is desirable that wireless transceivers for use with cellular telephones or personal computing devices should be sized for portability and convenient user experience. However, depending on the radio operating frequencies and required signal strengths involved, the products must exceed a certain minimum size in order to accommodate radio antennas of appropriate physical dimensions.
The limitations of conventional wireless transceiver products can be illustrated with particular respect to current wireless adapter systems, which provide plug-in wireless communications capabilities to a host system such as a laptop computer. Common wireless adapters of this type may operate for example similarly to a cellular telephone or wireless network interface, having a wired data port for connection to a host system and including a radio transceiver. Such wireless adapters can therefore be considered to include three distinct parts, a data port, an intermediate electronics package, and an antenna.
For example, a wireless adapter of this type can be connected to provide wireless capabilities to a host computer through a standard interface such as a PCI, PCMCIA, Express Card, Firewire or USB interface. In the case of PCI, PCMCIA and Express Card interfaces, the adapter electronics section is typically located or enclosed substantially within a slot of the host system, and the antennas are located on a portion of the adapter external to the slot. In the case of a USB interface, the adapter electronics and antenna are typically both contained in a package external to the host system since the USB interface is only a relatively small connection port. The wireless adapter can also comprise one or more movable antenna portions which can increase design flexibility.
A problem with such wireless adapters is that it is often difficult to satisfy radio performance requirements simultaneously with small size requirements, for example to provide adequate radio performance with a convenient, low cost and portable unit. This can be especially challenging when a larger radio transceiver would be an asset, for example to provide radio performance at relatively lower frequencies, to provide increased power for radio transmission or reception, or to provide for multiple antennas such as can facilitate performance improvements due to diversity, multiple frequency operation, or separation of radio functions.
One approach to the above problem is to design specialized antenna structures inside the wireless adapter. By providing antenna elements having adequately precise dimensions and features, improved radio performance in certain predetermined frequency bands can be provided even within a small package. For example, in the case of a monopole antenna, an antenna body within the package, such as a patch antenna or a planar inverted F antenna (PIFA), can be radiated against a ground plane also contained within the package, for example the electronics ground plane connected through the data port to a host device. For example, United States Patent Application Publication Nos. 2007/0035452 and 2007/0044145 both describe a USB wireless adapter having an antenna radiating against an internal ground plane. In the case of a dipole antenna, two antenna bodies contained in the package radiate in combination. In each case, the dimensions of the antenna bodies and the effective antenna length are limited by the dimensions of the wireless transceiver package. In both cases, antenna dimensions and details can be important to operation. For example, self-similar antenna elements such as spiral or fractal elements can be tuned to offer adequate antenna performance at a variety of radio frequencies. However, design of such precision elements can be expensive, and the effective antenna power can still be limited due to size constraints.
Another approach to the above problems is to account for the external environment when designing antenna systems for wireless adapters. In particular, the environment near or even within the wireless adapter may contain electromagnetic elements such as electronics, ground planes, passive and active electromagnetic bodies, laptop components, and the like, which may interact or interfere with the wireless adapter radio components. To the extent that it is possible to predict and plan for these elements, their presence can be accounted for to design a radio communication apparatus with improved radio performance.
However, a potential drawback to designing a wireless adapter for a particular environment is that it may be substantially limited to that environment. For example, as illustrated in FIG. 1, a USB wireless adapter 100 may be specifically designed to be plugged directly into the side of a host such as a laptop computer 110. The USB wireless adapter may further be configured for operation in close proximity with metallic elements of the computer, for example in proximity to a laptop ground plane. However, performance of such a wireless adapter may significantly degrade if the adapter is not plugged directly into the host. For example, by using a cable to connect the wireless adapter to the host in order to place the adapter in a different position such as near a window to improve reception, or away from the laptop so as to reduce the specific absorption rate (SAR) of radio energy with respect to a user. In addition, use of a host with insufficient or excessive metallic elements may result in degradation of radio performance. Thus, adapting a wireless adapter for use in a predetermined environment may reduce its ability to be used in other environments.
Another constraint in the design of wireless communications packages comprising both electronics and radiating antenna bodies is that grounded and/or shielded components are often required, both to facilitate operation of the electronics, and to provide isolation between the electronic components and the antenna. However, such grounded components can also operate for example as de-tuning and de-sensing elements for the antenna, thereby compromising antenna operation.
Another potential drawback to operating a wireless adapter in close proximity to the host system, for example plugged directly into the host system, is that the electronics of the host system may interfere with operation of the wireless adapter.
Another potential drawback to operating a wireless adapter in close proximity to the host system such as a laptop is that the wireless adapter may also be in close proximity to a user, such that radiation from the wireless adapter may be absorbed at a rate exceeding a prescribed maximum specific absorption rate (SAR).
Therefore there is a need for a wireless communications system for coupling with an external system, such as a wireless adapter, that is not subject to one of more limitations of the prior art.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.